Mid-range and high performance computer systems comprise hundreds to thousands of integrated circuit (IC) chips and employ a variety of ways of interconnecting the IC chips. These systems also employ various types of interconnect substrates, such as for example, printed circuit boards and cards, and interconnect substrates of multi-chip modules.
In one interconnect approach, the IC chips are packaged in individual carriers and are distributed on a number of printed-circuit-board (PCB) cards, with each card being "plugged" into a main interconnect PCB board through a card-to-board connector. Each PCB card includes interconnecting electrical traces, or lines, which route electrical power to the IC chips, and which also route electrical signals between the card's IC chips and between the IC chips and the main interconnect board. A card-to-board connector may comprise a conventional leaf-spring tab connector, a zero-insertion-force (ZIF) connector, or a conductive elastomer connector compressed between the components. Alternatively, the connector may be eliminated and the traces on PCB card formed to enable direct soldering to corresponding traces on the main interconnect board.
In another approach, the IC chips are distributed on a plurality of multi-chip modules and mounted thereto without individual chip packaging. Each module in turn is "plugged" onto a main interconnect board, forming a two-dimensional array with the other modules. Each multi-chip module comprises an interconnect substrate having two or more integrated circuit (IC) chips directly mounted thereto. A plurality of interconnect traces are formed in the module's substrate. There may be several thousand or more interconnect traces in a module. Some of the traces route power to the module's IC chips, while other traces route electrical signals between the module's IC chips. Still other traces carry electrical signals to other modules and input and output (I/O) signals to the system by way of the main interconnect board. In general, electrical signals propagate at higher speeds in the multichip modules than in the main interconnect board or in the PCB cards of the first approach.
A third approach distributes individually packaged IC chips on a number of like PCB cards which are stacked upon one another to form a three-dimensional chip array. Electrical power is fed to one face of the array, and system input/output (I/O) signals are fed to another face. A number of inter-layer interconnections extend vertically through the stacked PCB cards to couple electrical signals between the PCB cards. Currently, there is an interest in exploring ways in which this configuration might be applied to multi-chip modules.
In comparison to personal computers and workstations, high-performance computer systems employing the above approaches have relatively high numbers of signal connections between their PCB cards or modules and their main interconnect boards. Approximately 1,800 and more connections per board or module are typical in current products. In order to reduce the transit times of electrical signals and increase computation rates, current trends in the industry are to increase the number of these connections beyond present levels and to shrink the size of the cards, boards, and modules. Satisfying both of these trends will require a very large increase in the density of the connections. For the next generation of high-performance computers, it is expected that the connection density for two-dimensional multichip modules will have to increase two to four times from present levels of 30 to 60 connections per square centimeter of the module's connecting face. Of course, as the connection density increases, the connections themselves will need to have more precise dimensions and better alignment to corresponding connections. In turn, the modules, cards and boards will also need to have more precise dimensions and better alignment to mating components. As an economic matter, the increase in connection density will have to be achieved without substantial increases in manufacturing costs or in manufacturing complexity, the latter of which may adversely impact on the yield of modules, cards, boards, and connectors.
Unfortunately, there are a number of barriers which hinder achieving increased connection densities, more precise dimensions of the connections, and better alignments of the connections. The electrical traces formed through many multichip modules, cards, boards, and connectors currently have relatively narrow widths in comparison to their lengths, and accordingly have what will be referred to herein as high aspect ratios, which is defined as the ratio of the length of a trace divided by its average width. The traces are typically formed by punching, drilling, or molding, each of which uses a hole-forming tool having relatively narrow width in comparison to its length. Increasing the connection density will require decreasing the widths of the traces, which leads to increased aspect ratios for those traces whose lengths are not commensurately decreased. Unfortunately, it becomes more difficult to form the traces as the aspect ratio increases because the increased aspect ratio of the hole-forming tool causes the tool to become more prone to deflecting off course during the formation process, causing misalignment of the trace, unwanted merging of traces, or breakage of the tool inside the card, board, or module. Typically, conventional connectors are limited to trace aspect ratios of approximately 20 or less.
Furthermore, in those cases where card-to-board connectors are used to couple various components, it becomes more difficult to manufacture the connectors with precise dimensions and to connect them to their respective components as the connection density increases simply because the sizes of the connector's electrical parts (e.g., leaf springs and pins) decrease. It is also more difficult to align the card-to-board connectors, as many of these connectors have interconnecting parts which are not sufficiently rigid and may therefore move (e.g., leaf spring tabs, elastomer connectors). This movement, particularly in rubber elastomer connectors, can result in incorrect placement of mating circuit boards, either initially or over time due to vibrations, contact forces, or stresses caused by thermal expansion and contraction. Some connectors simply lack the rigidity needed to maintain the dimensional integrity required for the high density of connections.
Accordingly, there is a need for connectors having precise dimensions and trace placements so as to ensure accurate interconnection of traces among interconnect substrates (e.g., cards, boards, and module substrates). Additionally, connectors having traces with high aspect ratios formed without complex or costly manufacturing processes are desirable. It would further be advantageous to have card-to-board connectors, board-to-board connectors, and main interconnect boards for multichip modules which can employ various connection schemes, particularly ones which would permit easy configuration changes.